Low-power ethernet device

ABSTRACT

In accordance with the teachings of this disclosure, an Ethernet device is provided that draws current below a predetermined voltage, and as the voltage across the device exceeds the threshold, the device transforms into a high-impedance state, appearing as a high impedance device. Once in the high-impedance state, the discovery process proceeds normally as the current drawn through the high-impedance device is no more than normally occurs due to leakage or other typical conditions. Thus, the IEEE discovery now proceeds normally in the higher voltage ranges (6V to 9V) where the device of this disclosure is effectively out of the circuit, causing no interference.

FIELD OF THE INVENTION

The present invention relates generally to networking equipment, whichis powered by, and/or powers other networking equipment over wired datatelecommunications network connections.

BACKGROUND OF THE INVENTION

Inline Power (also known as Power over Ethernet and PoE) is a technologyfor providing electrical power over a wired telecommunications networkfrom power source equipment (PSE) to a powered device (PD) over a linksection. The power may be injected by an endpoint PSE at one end of thelink section or by a midspan PSE along a midspan of a link section thatis distinctly separate from and between the medium dependent interfaces(MDIs) to which the ends of the link section are electrically andphysically coupled.

PoE is defined in the IEEE (The Institute of Electrical and ElectronicsEngineers, Inc.) Standard Std 802.3af-2003 published 18 Jun. 2003 andentitled “IEEE Standard for Information technology—Telecommunicationsand information exchange between systems—Local and metropolitan areanetworks—Specific requirements: Part 3 Carrier Sense Multiple Accesswith Collision Detection (CSMA/CD) Access Method and Physical LayerSpecifications: Amendment: Data Terminal Equipment (DTE) Power via MediaDependent Interface (MDI)” (herein referred to as the “IEEE 802.3afstandard”). The IEEE 802.3af standard is a globally applicable standardfor combining the transmission of Ethernet packets with the transmissionof DC-based power over the same set of wires in a single Ethernet cable.It is contemplated that Inline Power will power such PDs as InternetProtocol (IP) telephones, surveillance cameras, switching and hubequipment for the telecommunications network, biomedical sensorequipment used for identification purposes, other biomedical equipment,radio frequency identification (RFID) card and tag readers, securitycard readers, various types of sensors and data acquisition equipment,fire and life-safety equipment in buildings, and the like. The power isdirect current, 48 Volt power available at a range of power levels fromroughly 0.5 watt to about 15.4 watts in accordance with the standard.There are mechanisms within the IEEE 802.3af standard to allocate arequested amount of power. Other proprietary schemes also exist toprovide a finer and more sophisticated allocation of power than thatprovided by the IEEE 802.3af standard while still providing basiccompliance with the standard. As the standard evolves, additional powermay also become available. Conventional 8-conductor type RJ-45connectors (male or female, as appropriate) are typically used on bothends of all Ethernet connections. They are wired as defined in the IEEE802.3af standard.

FIGS. 1A, 1B and 1C are electrical schematic diagrams of three differentvariants of PoE as contemplated by the IEEE 802.3af standard. In FIG. 1Aa data telecommunications network 10 a comprises a switch or hub 12 awith integral power sourcing equipment (PSE) 14 a. Power from the PSE 14a is injected on the two data carrying Ethernet twisted pairs 16 aa and16 ab via center-tapped transformers 18 aa and 18 ab. Non-data carryingEthernet twisted pairs 16 ac and 16 ad are unused in this variant. Thepower from data carrying Ethernet twisted pairs 16 aa and 16 ab isconducted from center-tapped transformers 20 aa and 20 ab to powereddevice (PD) 22 a for use thereby as shown. In FIG. 1B a datatelecommunications network 10 b comprises a switch or hub 12 b withintegral power sourcing equipment (PSE) 14 b. Power from the PSE 14 b isinjected on the two non-data carrying Ethernet twisted pairs 16 bc and16 bd. Data carrying Ethernet twisted pairs 16 ba and 16 bb are unusedin this variant for power transfer. The power from non-data carryingEthernet twisted pairs 16 bc and 16 bd is conducted to powered device(PD) 22 b for use thereby as shown. In FIG. 1C a data telecommunicationsnetwork 10 c comprises a switch or hub 12 c without integral powersourcing equipment (PSE). Midspan power insertion equipment 24 simplypasses the data signals on the two data carrying Ethernet twisted pairs16 ca-1 and 16 cb-1 to corresponding data carrying Ethernet twistedpairs 16 ca-2 and 16 cb-2. Power from the PSE 14 c located in themidspan power insertion equipment 24 is injected on the two non-datacarrying Ethernet twisted pairs 16 cc-2 and 16 cd-2 as shown. The powerfrom non-data carrying Ethernet twisted pairs 16 cc-2 and 16 cd-2 isconducted to powered device (PD) 22 c for use thereby as shown. Notethat powered end stations 26 a, 26 b and 26 c are all the same so thatthey can achieve compatibility with each of the variants describedabove.

Turning now to FIGS. 1D and 1E, electrical schematic diagrams illustratevariants of the IEEE 802.3af standard in which 1000 BaseT communicationis enabled over a four pair Ethernet cable. Inline Power may be suppliedover two pair or four pair. In FIG. 1D the PD accepts power from a pairof diode bridge circuits such as full wave diode bridge rectifier typecircuits well known to those of ordinary skill in the art. Power maycome from either one or both of the diode bridge circuits, dependingupon whether Inline Power is delivered over Pair 1,2, Pair 3,4 or Pair4,5, Pair 7,8. In the circuit shown in FIG. 1E a PD associated with Pair1-2 is powered by Inline Power over Pair 1-2 and a PD associated withPair 3-4 is similarly powered. The approach used will depend upon the PDto be powered. Inline Power is also available through techniques thatare non-IEEE 802.3 standard compliant as is well known to those ofordinary skill in the art.

In order to provide regular Inline Power to a PD from a PSE it is ageneral requirement that two processes first be accomplished. First, a“discovery” process must be accomplished to verify that the candidate PDis, in fact, adapted to receive Inline Power. Second, a “classification”process must be accomplished to determine an amount of Inline Power toallocate to the PD, the PSE having a finite amount of Inline Powerresources available for allocation to coupled PDs.

The discovery process looks for an “identity network” at the PD. Theidentity network is one or more electrical components that respond incertain predetermined ways when probed by a signal from the PSE. One ofthe simplest identity networks is a resistor coupled across the twopairs of common mode power/data conductors. The IEEE 802.3af standardcalls for a 25,000 ohm resistor to be presented for discovery by the PD.The resistor may be present at all times or it may be switched into thecircuit during the discovery process in response to discovery signalsfrom the PSE.

The PSE applies some Inline Power (not “regular” Inline Power, i.e.,reduced voltage and limited current) as the discovery signal to measureresistance across the two pairs of conductors to determine if the 25,000ohm resistance is present. This is typically implemented as a firstvoltage for a first period of time and a second voltage for a secondperiod of time, both voltages may exceed a maximum idle voltage (0-30VDC in accordance with the IEEE 802.3af standard and can reach a maximumof 30 v) which may be present on the pair of conductors during an “idle”time while regular Inline Power is not provided. The discovery signalsdo not enter a classification voltage range (typically about 15-20V inaccordance with the IEEE 802.3af standard) but have a voltage betweenthat range and the idle voltage range. The return currents responsive toapplication of the discovery signals are measured and a resistanceacross the two pairs of conductors is calculated. If that resistance isthe identity network resistance, then the classification process maycommence, otherwise the system returns to an idle condition.

In accordance with the IEEE 802.3af standard, the classification processinvolves applying a voltage in a classification range to the PD. The PDmay use a current source to send a predetermined classification currentsignal back to the PSE. This classification current signal correspondsto the “class” of the PD. In the IEEE 802.3af standard as presentlyconstituted, the classes are as set forth in Table I:

TABLE I PSE Classification Corresponding Class Current Range (mA) InlinePower Level (W) 0 0-5 15.4 1  8-13 4.0 2 16-21 7.0 3 25-31 15.4 4 35-45Reserved

The discovery process is therefore used in order to avoid providingInline Power (at full voltage of −48VDC) to so-called “legacy” devices,which are not particularly adapted to receive or utilize Inline Power.

The classification process is therefore used in order to manage InlinePower resources so that available power resources can be efficientlyallocated and utilized.

The IEEE 802.3af standard, however, does not provide for a device to bepowered at low levels, i.e., below about 5V prior to the discoveryprocess being completed, 802.3af allows a PSE to deliver no more than 5mA while detection is active, this assumes a single PD attached to asingle PSE. If more than one PD needs to connect to a single PSE (in aserial fashion), the order of such connectivity to the PSE affects thecomplexity and the ability of the PSE to discover the presence or‘introduction’ of the 25 kΩ resistor that is now present while anadditional PD is drawing low-level currents.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated into and constitute apart of this specification, illustrate one or more embodiments of thepresent invention and, together with the detailed description, serve toexplain the principles and implementations of the invention.

FIGS. 1A, 1B, 1C, 1D and 1E are electrical schematic diagrams ofportions of data telecommunications networks in accordance with theprior art.

FIG. 2 is an electrical schematic diagram of a typical Ethernet 10/100Base T connection in accordance with the prior art.

FIG. 3 is a block diagram of an Ethernet powered device configured inaccordance with this disclosure.

FIG. 4 is an exemplary schematic diagram of an Ethernet powered deviceconfigured in accordance with the teachings of this disclosure.

FIG. 5 is an exemplary schematic diagram of an Ethernet system includinga powered device configured in accordance with the teachings of thisdisclosure.

FIG. 6 is an exemplary schematic diagram of an Ethernet system capableof supplying data and inline power supporting the embodiment disclosedherein.

FIG. 7 is an exemplary schematic diagram of an Ethernet system capableof supplying 10/100 Ethernet data and inline power on one set of pairsin a single cable.

FIG. 8 is an exemplary schematic diagram of an Ethernet splitter-dongleembodiment.

FIG. 9 is an exemplary schematic diagram of an Ethernet redundancyapplication.

DETAILED DESCRIPTION

Embodiments of the present invention described in the following detaileddescription are directed at a low-power Ethernet powered device. Thoseof ordinary skill in the art will realize that the detailed descriptionis illustrative only and is not intended to restrict the scope of theclaimed inventions in any way. Other embodiments of the presentinvention, beyond those embodiments described in the detaileddescription, will readily suggest themselves to those of ordinary skillin the art having the benefit of this disclosure. Reference will now bemade in detail to implementations of the present invention asillustrated in the accompanying drawings. Where appropriate, the samereference indicators will be used throughout the drawings and thefollowing detailed description to refer to the same or similar parts.

In the interest of clarity, not all of the routine features of theimplementations described herein are shown and described. It will, ofcourse, be appreciated that in the development of any such actualimplementation, numerous implementation-specific decisions must be madein order to achieve the developer's specific goals, such as compliancewith application- and business-related constraints, and that thesespecific goals will vary from one implementation to another and from onedeveloper to another. Moreover, it will be appreciated that such adevelopment effort might be complex and time-consuming, but wouldnevertheless be a routine undertaking of engineering for those ofordinary skill in the art having the benefit of this disclosure.

Turning now to FIG. 2 a typical 2-pair Ethernet (10 Base T, 100 Base Tand 1000BT if 4-pairs were used) connection is illustrated. Box 100encompasses the Ethernet port as it might exist in a network device suchas a switch, hub, router or like device. Within port 100 is a PHY orphysical layer device 102, which includes transmit circuitry 104 andreceive circuitry 106. The transmit circuitry 104 interfaces to aconnector such as an RJ-45 connector (not shown here) and through theconnector to a cable 108 which includes at least two pairs ofconductors, the Pair 1-2 (110) and the Pair 3-6 (112). The interfacebetween the transmit circuitry 104 and the cable 108 includes acenter-tapped magnetic device such as transformer T1. T1 has a PHY-sideincluding pins 1 and 2 and center tap 6, and a wire side including pins3 and 5 and center tap 4. The PHY side is also referred to as theprimary side; the wire side is also referred to as the secondary side ofthe magnetic device T1. Termination circuitry 114 provides a Vdd bias(here illustrated as +3.3VDC) to the primary of T1. The secondary of T1is coupled to cable pair 112 which is, in turn, coupled in operation toa network device 118 which may be another hub, switch or router or a PDsuch as a Voice Over Internet Protocol (VOIP) telephone or other networkdevice.

The interface between the receive circuitry 106 and the cable 108includes a center-tapped magnetic device such as transformer T2. T2 hasa PHY-side including pins 1 and 2 and center tap 6, and a wire sideincluding pins 3 and 5 and center tap 4. The PHY side is also referredto as the primary side; the wire side is also referred to as thesecondary side of the magnetic device T2. Termination circuitry 116provides a ground bias to the primary of T2. The secondary of T2 iscoupled to cable pair 110 which is, in turn, coupled in operation to anetwork device 118. If the pairs of conductors shown belonged to a 1000Base T wired data telecommunications network segment then each pairwould transmit and receive at the same time and all four pairs in thecable would be used.

Center tap pins 4 of T1 and T2 are coupled to inline power circuitryincluding a 48 VDC power supply 120 for providing Inline Power overcable 108, control circuitry 122 and switch circuitry 124.

As mentioned above, the Ethernet specification does not provide forpowering a load, such as an LED, sensor, or other load, that requiressourcing power from the switch below 5V (other than powering a phone).It is contemplated that a device may be desirable that must source powerin the range of a few to tens of milliamps of current in the range ofapproximately 3.3V-5V. It is further contemplated that such a device maybe active prior to 48V being applied, and becomes inactive when the 48Vis applied and no longer requires current.

The present disclosure provides for a special device that may receivecurrent from an Ethernet switch at lower voltage levels, i.e., betweenapproximately 3.3V to 5V, but at the same time allowing proper Ethernetdiscovery of a normal powered device (such as a phone) including a 25 kΩdiscovery resistance.

To illustrate the problem presented, we may assume that an LED isdesired to be illuminated. In this case, the system must bias seriesdiodes while the switch searches for a 25 kΩ resistance to be pluggedin. The switch faces the challenge of resolving the slope (i.e.,calculating the slope=dV/di as described earlier) since approximately170 μA and 300 μA, (if a force-current based discovery is used) must bedetected and resolved out of the approximately 3 mA or possibly highercurrent levels This is a difficult task for a circuit designed toresolve 300 μA while discovery is active in order to find the 25 kΩsignature resistance while in parallel. The present disclosure providesa lower impedance path on that same circuit in order to deliver the 3 mAcurrent of higher current required for the device of this disclosure.

The present disclosure provides for a powered device that can coexistwith present 802.3af PD based Ethernet systems such that the 25 kΩdiscovery process properly take place without the need to resolvecurrent levels having ratios of approximately 10:1. The presentdisclosure thus provides the benefits of a lower-power device withoutthe requirement for higher resolution (and higher cost) circuitry, whileenabling an extra load to draw power at the same time in the absence ofa conventional PD.

In accordance with the teachings of this disclosure, a device isprovided that draws current below a predetermined voltage, and as thevoltage across the device exceeds the threshold, the device transformsinto a high-impedance state, appearing as a high impedance device. Oncein the high-impedance state, the discovery process proceeds normally asthe current drawn through the high-impedance device is no more thannormally occurs due to leakage or other typical conditions. Thus, theIEEE 802.3af discovery process now proceeds normally in the highervoltage ranges (6V to 9V) where the device of this disclosure iseffectively out of the circuit, causing no interference. A low-powereddevice in accordance with this disclosure may deploy a local capacitoracting as a temporary power supply while the attached PSE does aback-off routine (executes a discovery cycle where it forces the deviceto become high impedance and temporarily aborts its current draw).

As will now be appreciated, the device of this disclosure may now beclassified as an Ethernet powered device in IEEE terminology.Additionally, as the disclosed device draws a distinctive amount of DCcurrent, the value of the DC current it draws may be used as anadditional signature and classification value that provides a commonmode signature that can coexist with the 25 kΩ signature resistance. Asthe device of this disclosure may be found below 5V, the presence of aspecial powered device may be flagged in accordance with the teachingsof this disclosure. Thus, the fact that the disclosed device draws powerat a low voltage and draws no power above a certain threshold when in ahigh-impedance state, may itself provide a unique signature andclassification scheme. Likewise, the other current drawing scenariosoccurring in other voltage ranges of this disclosure may also be used todefine other discovery/classification schemes.

For example, while this disclosure demonstrates the use of a PSE voltagebelow 5V in order to supply power to a device similar to PD1 as shown inFIG. 6, other voltage ranges may be applicable such as 10-15V or 20-30Vwhere a PSE might deliver more current to powered PD1, while keepingboth the IEEE 802.3af discovery and classification circuitry andimplementations compliant with the standard and the complexity of thePSE circuitry under control.

It is contemplated that multiple devices similar to PD1 may be connectedin series with an 802.3af-compliant PD that would present a 25 kΩsignature resistor. As disclosed herein, the devices are configured toenter a high impedance state in the specified detection ranges (0-5V)and somewhere between 12-15V and 20-30V. The amount of devices that maybe chained in accordance with this disclosure is limited by the amountof leakage that affects the discovery process and whether the discoveryprocess uses the applied voltage measure current method or the forcecurrent measure voltage method. Another limitation on such a cascadingscheme would be the multiple autotransformers present in parallel thatwould affect (lower) the inductance of the loop and burden the reliabletransfer of data.

For example, if low-power device has a window comparator to allow it topresent its load and signature to the PSE between 10 to 15V or 20-30V,the same results may be achieved. Also, the IEEE spec allows the maximumdetection voltage to reach 30V with limited current, a pseudo-compliantPD and PSE devices may be designed to meet the specification of IEEE802.3af and enable a host of pseudo-compliant PD devices similar to PD1and in different voltage ranges may be exploited where the IEEE 802.3afdoes not define the behavior of a PD.

FIG. 3 is a block diagram of an Ethernet powered device 300 configuredin accordance with this disclosure. FIG. 3 shows the device 300including threshold detect circuitry 310 for monitoring the voltageacross two pairs in a cable. In a preferred embodiment, the device 300is coupled between two pairs in a cable through the common mode nodes apair of autotransformers 335 and 340 formed by coils L1 and L2, and L3and L4, respectively. The device 300 may be coupled to theautotransformers through a DC return rail 325 and a negative rail 330.The device 300 is shown as being coupled between pairs 3,6 and 1,2, butof course the device 300 may be coupled between other pairs as desired.

In a preferred embodiment, the threshold detect circuitry 310 isconfigured to monitor the voltage across the cable pairs through theautotransformers in order to detect a level that is higher than apredetermined threshold. In a preferred embodiment, the threshold maycomprise a level that is within the IEEE detection window but outside ofthe range of voltages used by a specific PSE. The IEEE detectionvoltages as specified in the IEEE 802.3af specification are valid up to30V, while a valid IEEE PD may draw classification current in the rangeof 15-20V, 802.3af leaves windows of usable voltage ranges between10-15V, and 20-30V, where 310 would be designed to enable Rload 320 todraw current in these ranges (10-15V and 20-30V) while turning into ahigh impedance load outside these ranges. In this disclosure, thepreference is given to the range below 5V to keep the cost of the PDcircuitry low and avoid the cost and complexity resulting from the needof voltage converters to reduce the voltage potential back to the morecommon values of 5V or lower where inexpensive components can beacquired.

It is also possible that a low-powered device in accordance with theteachings of this disclosure may make use of more than one range ofvoltage to draw power. For example, the device may draw power below 5V,while being placed in a high impedance state in both the detection andclassification voltage ranges as defined in IEEE 802.3af, while alsobeing operable in either or both of the 10-15V and 20-30V ranges.

The device 300 further includes a switch 315 coupled with a load 320.The switch 315 is preferably configured to selectively couple the load320 to the rails 325 and 330, thereby selectively isolating the load 320from the PSE. In a further preferred embodiment, the switch 315 isoperated under control from the threshold detect circuitry 310. It iscontemplated that when the voltage as sensed by the threshold detectcircuitry 310 is below a threshold, the load 320 will be switched in viathe switch 315, thereby allowing current to be sourced by the load 320.When the sensed voltage exceeds a threshold, the load 320 will beisolated from the system when switch 315 opens, allowing the discoveryprocess to proceed normally i.e. to discover the 25 kΩ signatureresistance presented without the risk of performance complications dueto the dynamic range requirements on resolving the 300 μA current out ofa 3 mA or higher current.

FIG. 4 is an exemplary schematic diagram of an Ethernet powered device400 configured in accordance with the teachings of this disclosure. FIG.4 includes a voltage source 410, representing the power source of thePSE to which the device 400 would normally be coupled. The voltagesource 410 is shown being coupled through positive and negative rails411 and 412, respectively, to a signature resistor Rsig, representingthe 25 kΩ signature resistance of the PD to which the device 400 wouldnormally be attached.

The device 400 includes a first circuit branch 440 configured tofunction as the threshold detection circuitry described above. In apreferred embodiment, the first branch includes a 10 MΩ resistor 415coupled to the positive rail 411. Coupled to the resistor 415 are a pairof diodes 420 and 425. Coupled between the diode 425 and the negativerail 430 is a zener diode 430.

The device 400 includes a second branch 450 configured to selectivelyisolate a load based on conditions sensed by the first branch 440 ofthreshold sensing circuitry. The second branch includes a resistor Rloadrepresenting the load to be powered. The load is shown as a resistanceto model the effect, though loads of any equivalent effectiveresistances may be powered using different circuit configurations. Theload is shown as being coupled to the positive rail 411. Coupled to theRload in series is a transistor M1, illustrated as comprising anN-channel depletion transistor. M1 preferably comprises a switch that isnormally closed when no power is applied; other switches may beemployed.

Coupled between the transistor M1 and the negative rail is a switch J1,shown as comprising a P-channel switch. The gate of J1 is coupled to thenode between the zener diode 430 and diode 425. J1 is provided for addedprotection of M1; other devices and configurations such as a zener diodeand diode to prevent reverse voltages from being applied may beemployed.

In operation, the depletion switch M1 and switch J1 are normally closedwhen no voltage is applied. In this state, current may be sourced by theload through the second branch 450. As the applied voltage rises aboveapproximately 5V, the switch J1 will open up, removing the second branchfrom the negative rail 412 and thereby removing the Rload from thecircuit. The device 400 will now be placed in a high impedance state. Atthis point, the only current flowing through the device 400 will be theminimal current flowing through the 10 MΩ resistor. Current will thus befree to flow through the signature resistor Rsig, thus allowing thediscovery process to proceed normally.

FIG. 5 is an overall schematic diagram showing a powered device disposedbetween a pair of Ethernet devices in accordance with this disclosure.FIG. 5 shows a pair of PHYs 510 and 520 coupled through Ethernet cablepairs 3,6 and 1,2. On the switch side, IEEE discovery circuitry 550 isshown being coupled to pairs 3,6 and 1,2 through magnetic couplingcircuitry XTX and XRX, respectively. Likewise, the PD side is shownincluding inrush control circuitry 560, a 25 kΩ signature resistor 565,coupled to pairs 3,6 and 1,2 through magnetic XRCV and XTXPD,respectively.

FIG. 5 illustrates a powered device 530 of this disclosure being coupledbetween a switch and a powered device. As disclosed above, the powereddevice 530 is shown as including the extra load 540 that is coupled topair 3,6 through coils L1 and L2, and pair 1,2 through coils L3 and L4.FIG. 5 also shows that the device of this disclosure may be coupledbetween two Ethernet devices through the use of standard connectors,such as RJ45B and RJ45C connectors as illustrated in FIG. 5.

FIG. 6 is an exemplary schematic diagram of an Ethernet system 600capable of supplying data and inline power supporting the embodimentdisclosed herein. PSE 610 may produce two test voltages in the 6-10Vrange, while it measures the current at each of the voltages supplied tocalculate the dV/di ratio in search of a 25 kΩ resistor 694. Inaccordance with the teachings of this disclosure, the PD1 640 may beembodied as a patch panel with an LED to flag the presence of inlinepower, a dongle that acts as a pair splitter that indicates the presenceof inline power on 4-pairs, or a mid-span system flagging the presenceof inline power on the ‘unused’ pairs (4,5 and 7,8).

PD1 may draw milli-amp ranges of current below 5V or the range ofvoltages chosen as discussed in this disclosure through its load and‘signature’ 644 (presented here as a resistor). When device 680 isplugged into PD1, PSE 610 may be doing periodic checks for the‘introduction’ of PD2 by going above 6V and measuring the load currentand may opt to stay above 6V for several milliseconds of time beforereturning to a lower voltage if it recognizes no valid signature (25kΩ).

Also PSE 610 may rely on other means to start a detection cycle keepingthe power to PD1 steady and undisrupted. Such means may comprise asingle pair identity network present across pair 1,2 and/or pair 3,6(696, 692) as shown in 680 of FIG. 6, or a differential identity network698 as presented in device 680 and discovered by PHY 620 in the Ethernetsystem 600.

FIG. 7 is an exemplary schematic diagram of an Ethernet system 700capable of supplying 10/100 Ethernet data and inline power on one set ofpairs in a single cable through each single RJ45 connector or the like.Cable 710 connects such a system to a mid-span power system. A mid-spanpower system as known in the art is a system where typically two pairsin a cable are effectively ‘cut’ and power is imposed on them to bedelivered to a PD 750, such as an IP telephone or similar device overcable 730. The mid-span power injector may present a PD1 780 to PSE1over pairs 1,2 and 3,6 as shown in 720. The presence of this special PD1allows PSE1 to identify the presence of the midspan and the signaturesupplied by PD1 may be used to instruct PSE1 to never supply power evenif it discovers the 25 kΩ signature resistance.

Also the power available from the midspan may be encoded in the‘signature’ value of PD1. Lastly, the midspan may dynamically alter thestate of the signature presented by PD1 to enable inline power from PSE1for a redundancy application and the like.

FIG. 8 is an exemplary schematic diagram of an Ethernet splitter-dongle808 capable of taking data and inline power from an Ethernet system 800over a single cable 812 into a single RJ45 814 and ‘splitting’ orrouting 10/100 data and inline power to two different RJ45 connectors,840 and 860, enabling connectivity to two different devices 844 and 864respectively over two different cables 842 and 862. Two devices similarto PD1 as described above may be deployed inside such a splitter on eachset of pairs to enable the 800 Ethernet system to identify the presenceof such a splitter device while providing an LED light as a part of PD1to indicate to the user the availability of data and or inline power oneach set of pairs.

Also PD1 810 and 820 may be configured to include interdependentcircuitry such that if inline power is applied on one set of pairs 810,the signature and class provided by 820 may be changed to instruct theproper PSE present in 800 not to supply power or perform certain tasks.This concept is similar to the example shown in FIG. 7 for the midspan.

FIG. 9 is an exemplary schematic diagram of an Ethernet redundancyapplication where a special PD1 device is used to enable data and powerflow from one Ethernet system at a time while providing a high impedanceor no loading state to the standby system. A dongle device 900 acceptsdata and power from two different systems over two different cables intoRJ45-A 910 and RJ45-B 920. The presence of PD1 930 allows both systemsto detect the presence of such a redundancy enabling device. To keep thedisclosure brief not all conditions are examined that detail theinterference caused by the possibility of two different PSE devices (notshown) attached to 910 and 920 may cause interference in the detectionof PD1 (i.e., one PSE may be doing a 25 kΩ signature detection checkcausing the other PSE attached to initiate its own detection cycle sinceit could not see device 930).

The presence of these single pair identity networks may define themaster/slave relationship between the devices attached to 910 and 920supplying data and inline power. Once device 930 has been designated asa load (and agreement is reached as to whether the PSE attached to 910or 920 is the master) it plays an important role in drawing enough DCcurrent to ‘bias’ the four diodes (present in the signal path, such asDTAP, DTAN, and DRAP, DRAN) ON, thus enabling the AC data signals toflow from the master Ethernet device present. This allows legacy devicesattached to connector 940 or RJ45-C to communicate with the master dueto the presence of diodes that otherwise may not conduct full cycle.

Thus, the role of PD1 here is to enable communication between the activedata device acting as master attached to either 910 or 920 while theslave awaits for an enable command that configures it as the master byinstructing it to deliver its own DC current to bias the diode on andsatisfy the load presented by 930 thus enabling communication and powerdelivery from either one of the devices attached to 910 or 920 to athird device attached to 940 over a third cable upon request.

The presence of multiple low power devices between a single PSE/PDconnection may be detected and each of the attached devices directed todraw power in different voltage ranges as discussed in this disclosure.Power drawn by an attached device, when measured by the PSE outside thenormal 802.3af operational voltages of classification detection andnormal full supply modes, may be used to inform the PSE with informationabout the configuration of each the attached devices. For example, ifthe splitter draws power in the 10-15 v range, and an LED low power PDdraws power below 5 v, the PSE now knows that there are two more devicesin addition to the 802.3af attached PD if present and acts accordingly.While few examples of such low power devices have been described,numerous applications of this concept for different devices andconfigurations are within the scope of this disclosure.

While embodiments and applications of this invention have been shown anddescribed, it will now be apparent to those skilled in the art havingthe benefit of this disclosure that many more modifications thanmentioned above are possible without departing from the inventiveconcepts disclosed herein. Therefore, the appended claims are intendedto encompass within their scope all such modifications as are within thetrue spirit and scope of this invention.

1. A low-power Ethernet-compatible powered device: anEthernet-compatible low-power device; the device being operable betweenan Ethernet Power Source Equipment (PSE) and an Ethernet Powered Device(PD); the low power device including: threshold detection circuitrydisposed between a return rail and a negative rail, the rails beingcoupled between respective pairs of an Ethernet cable coupling the PSEand PD; a load coupled inline with a switch between the return andnegative rails, the switch being in operative communication with thethreshold detection circuitry; and the threshold circuitry and switchbeing configured to allow the load to source current from the respectivepairs of Ethernet cables when the voltage sensed by the thresholdcircuitry is below a predetermined threshold, and place the load in ahigh impedance state when the sensed voltage exceeds the predeterminedthreshold.
 2. The device of claim 1, wherein said low power device isplaced in said high-impedance state when the applied voltage exceedsapproximately 5V.
 3. The device of claim 2, wherein said load of saiddevice sources current below approximately 5V.
 4. The device of claim 1,wherein said device is classified as an Ethernet powered device.
 5. Thedevice of claim 4, wherein said device draws a distinctive amount of DCcurrent in one or more voltage ranges outside the ranges specified bythe IEEE 802.3af standard for detection and classification, and whereinthe value of the DC current drawn within said voltage ranges acts asadditional signature and classification values for said device.
 6. Thedevice of claim 5, wherein multiple devices are coupled between said PSEand PD, and each of said devices operates in a different voltage range.7. The device of claim 5, wherein said device provides a common modesignature that coexists with the 25 kΩ signature resistance of a powerdevice connected to said device.
 8. The device of claim 6, wherein thecharacteristic of said device drawing power at a low voltage level anddrawing minimal power above a certain threshold when in a high-impedancestate provides a basis for a unique signature and classification schemecompatible with the IEEE 802.3af standard.
 9. The device of claim 8,wherein said current drawing characteristics are used to define aplurality discovery/classification schemes and device connectivityconfigurations in multiple voltage ranges.
 10. The device of claim 9,wherein said multiple voltage ranges comprise either of the voltageranges of 10-15V and 20-30V.
 11. A low-power Ethernet-compatible powereddevice: an Ethernet-compatible low-power device; the device beingoperable between an Ethernet Power Source Equipment (PSE) and anEthernet Powered Device (PD); and the low power device including meansfor allowing the load to source current from the respective pairs ofEthernet cables when a sensed voltage is below a predeterminedthreshold, and place the device in a high impedance state when thesensed voltage exceeds the predetermined threshold.
 12. The device ofclaim 11, wherein said low power device is placed in said high-impedancestate when the applied voltage exceeds approximately 5V.
 13. The deviceof claim 12, wherein said device sources current below approximately 5V.14. The device of claim 11, wherein said device is classified as anEthernet powered device.
 15. The device of claim 14, wherein said devicedraws a distinctive amount of DC current in one or more voltage rangesoutside the ranges specified by the IEEE 802.3af standard for detectionand classification, and wherein the value of the DC current drawn withinsaid voltage ranges acts as additional signature and classificationvalues for said device.
 16. The device of claim 15, wherein multipledevices are coupled between said PSE and PD, and each of said devicesdraws operates in a different voltage range.
 17. The device of claim 15,wherein said device provides a common mode signature that coexists withthe 25 kΩ signature resistance of a power device connected to saiddevice.
 18. The device of claim 16, wherein the characteristic of saiddevice drawing power at a low voltage level and drawing minimal powerabove a certain threshold when in a high-impedance state provides abasis for a unique signature and classification scheme compatible withthe IEEE 802.3af standard.
 19. The device of claim 18, wherein saidcurrent drawing characteristics are used to define a pluralitydiscovery/classification schemes and device connectivity configurationsin multiple voltage ranges.
 20. The device of claim 19, wherein saidmultiple voltage ranges comprise either of the voltage ranges of 10-15Vand 20-30V.
 21. A low-power Ethernet-compatible powered device: anEthernet-compatible low-power device; the device being operable betweenan Ethernet Power Source Equipment (PSE) and an Ethernet Powered Device(PD); the low power device including: means for allowing the load tosource current from the respective pairs of Ethernet cables when asensed voltage is below a predetermined threshold, and place the devicein a high impedance state when the sensed voltage exceeds thepredetermined threshold; and means for providing visual indicatorsregarding Ethernet power and data availability over sets of Ethernetcable pairs attached to said device.
 22. An Ethernet-compatible midspandevice: an Ethernet-compatible midspan device being operable between anEthernet Power Source Equipment (PSE) and an Ethernet Powered Device(PD); the midspan device being coupled to the PSE with a single cableand to one or more PDs, each coupled to the midspan device with arespective cable pair, the midspan device further comprising: means formanaging delivery of power on any of said set of pairs; means formodulating an IEEE 802.3af-compliant signature from one or more attacheddevices to a single PSE over a single cable; means for managingdetection and classification voltages and currents drawn from anattached PSE on one or more sets of pairs of an Ethernet cable to signalits presence; means for managing signal and attached deviceconfigurations information between said PSE and PD; means for disablingone or more loads from sourcing power from the respective pairs ofEthernet cables of an attached PSE when a sensed voltage is in a rangethat may cause detection and classification interference for said PSE;and means for enabling one or more loads to source power from said PSEby when said sensed voltage will not cause interference with thedetection and classification for said attached PSE.